Gerhard M. Sessler and James E. West are generally credited with the discovery in 1962 that certain plastic dielectric materials can be employed to advantage in electret microphones. Their electret permanently retained electrostatic charge and provided sufficiently low output impedance to operate with then conventional transistor amplifiers.
A number of manufacturers since 1962 have commercially made available compact packages wherein a semi-conductor amplifier and an electret microphone, in combination, provide an electrical signal in the audio frequency range.
In the movement toward further miniaturization of the electret microphone and amplifier combination, however, manufacturers have been impeded in their efforts to employ integrated circuit technology. The problem they have faced is that of applying integrated circuit technology to the generally high impedance (low capacitance) of small electret microphones. Also, it is especially useful for the integrated circuit amplifier to provide an overall gain to the output of the electret and provide an output impedance several orders of magnitude lower than the impedance of the electret.